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Chem 152 Chapter 5 Part 1: Early Atomic Theory and Structure. Sections 5.1 – 5.5 Dalton’s Atomic Theory Each element consists of indivisible*, minute particles called atoms. Atoms can neither be created or destroyed in chemical reactions. All atoms of a given element are identical*. Atoms combine in whole-number ratios to form compounds. Atoms of different elements have different masses. Numbers 1 and 3 are not completely correct! What’s Inside the Atom? Atoms are not indivisible! There are three types of “subatomic” particles inside each atom: Proton Neutron Electron Determined by many scientists, experiments over many years. Protons, Neutrons and Electrons Protons and neutrons are much heavier than electrons (1800x heavier). Electrical charge: Protons “positive” + Electrons “negative” – Neutrons “neutral” Protons and neutrons are located in the center of the atom in a densely packed “nucleus”. Electrons “fly around” outside the nucleus in a cloud-like area. Results of Rutherford’s Experiment Most of the mass of the atom is confined to a dense nucleus. The nucleus has a positive charge. The rest of the atom is mostly empty space. Protons Define an Element All atoms of the same element have the same number of protons. Hydrogen: 1 proton Carbon: 6 protons Oxygen: 8 protons Iron: 26 protons Lead: 82 protons The atomic number of an element is the same as its number of protons. Isotopes Atoms of the same element may have different numbers of neutrons. Carbon may have 6, 7 or 8 neutrons. Hydrogen may have 0, 1 or 2 neutrons. These are called isotopes. Most elements have more than one isotope. Some isotopes are radioactive. Unstable, decay into other elements. Example: Isotopes of Carbon Remember: Carbon (C) has an atomic number of 6. All C atoms have 6 protons. The proton and neutron both have a relative mass of 1. C may have 6, 7 or 8 neutrons. Therefore, the relative mass of a C atom will be 12, 13 or 14 depending on how many neutrons it has. This is called the mass number. These isotopes of carbon are called carbon-12, carbon-13 and carbon-14. We label them 12C, 13C and 14C. Which has more atoms: a one gram sample of carbon-12, or a one gram sample of carbon-13? Isotopes of Hydrogen hydrogen-1: protium hydrogen-2: deuterium hydrogen-3: tritium Mass Number To get the mass number of an isotope, simply add up the number of protons and neutrons. An atom with 11 protons and 12 neutrons has what mass number? What is the element? Complete the Following: Given the isotope 67Zn: Atomic # ?, Mass # ?, # of protons, # of neutrons, # of electrons Atomic Mass The total mass of an atom’s components (protons, neutrons and electrons) is call its atomic mass. Units: atomic mass unit: amu Each isotope of an element has a particular “natural abundance”. The percentage of each isotope found in a natural sample of the element. 12 C has a natural abundance of 98.89%. 13 Most of the rest is C. Atomic masses listed in the periodic table are averages of the atomic masses of each isotope. Atomic Mass Units 1/12 the mass of a carbon-12 atom. 1 amu = 1.6606 x 10 –24 g. All elements have atomic masses that are relative to carbon-12. Calculation of Average Atomic Mass (weighted average mass) Calculate the atomic mass of copper given the following data: 63Cu: 62.930 amu, 69.09% abundance 65Cu: 64.928 amu, 30.91% abundance (over all isotopes) fraction abundance x (exact weight) average mass = (0.6909)(62.930) + (0.3091)(64.928) Homework p. 131, Key Concepts: 2, 3, 4 p. 132, Exercises: 1 – 4, 11, 13, 15 – 27, 33 – 37.